While it is well known that the brain undergoes rapid developmental changes from birth to early childhood, remarkably little is understood about the relationship between changes in brain size and composition and cognitive development. Yet several potentially debilitating neurocognitive disorders are a consequence of delays or abnormalities in brain development, and childhood epilepsy has been shown to be associated with an increased risk of learning disabilities, attention-deficit hyperactivity disorder and depression. These associations make it imperative that we gain a better understanding of the relationship between cognitive and anatomical development. In children, the study of cognitive and brain developmental trajectories are best accomplished using non-invasive techniques that are not overly restrictive of movement and do not require ionizing radiation. Of available techniques, electroencephalography (EEG), particularly with the advent of high density sensor arrays, provides the ability to assess cognitive function safely and non-invasively. Our central goal is to develop age- specific pediatric head models to improve current source localization imaging in pediatric populations under the hypothesis that functional localization of cognitively important brain regions and networks requires an accurate model of head tissue geometry and conductivity. This Phase 2 project will build on work accomplished in phase 1 to create age clusters that differ significantly in measures of brain and skull development. For each cluster, we will build and test head models that are accurate both in morphological features and in regional differences in tissue conductivity which plays a critical role in the ability to accurately reconstuct brain network activity from EEG signals. Once age- specific average head models have been developed and tested, we will validate their improved accuracy based on neurophysiological data using EEG and functional magnetic resonance imaging methods in children from infancy to young adulthood. This project will result in the public release of a set of innovative age-specific head models together with newly developed software from our project website (www.pedeheadmod.net). In addition, the project will provide a novel commercial product, Child Geosource(R), which will allow source localization studies without the otherwise limiting need for CT or MR scanning for accurate head models.